1. Field of the Invention
The invention relates to optical sample detectors used in various fields of life and analytical sciences, in particular medical and biomedical assays. In particular, the invention relates to fluorescence-based sample analysers.
2. Prior Art
Fluorescence analysers or the present kind are commonly adapted to detect light successively from each one of a plurality of sample sites contained in the microplate. Therefore, they are frequently called as microplate “readers”. One example or such a system is the EnVision-reader and its variants available from PerkinElmer.
The present commercial microplate readers typically include a broad-band excitation light source. Before guiding the light emitted by the light source to a sample, the bandwidth of the light is regulated by filters, monochromators, or both. In prior art devices, high-quality dichroic filters and double monochromators are used.
US 2003/0081207 and U.S. Pat. No. 6,232,608 disclose devices including a plurality of optical filters and a monochromator arranged in series for selecting the desired wavelength. A disadvantage of such devices is that they require a large number of filters in order to be operable on a wide wavelength range. Therefore, if a new fluorescent marker, for example, is taken into use, also the filter bank of the device must be updated accordingly in order to get the best possible measurement results. However, the right filter having a sufficiently high quality may not always be at hand.
Devices having double monochromators installed in both the excitation and emission sides are disclosed in WO 00/63680 and US 2002/0109841. Double monochromators increase the wavelength-selectivity to a reasonable level but at the same time greatly increase the costs of the device.
WO 2005/057187 discloses a device having several different wavelength LEDs mounted to a rotatable wheel used as a moveable support, a rotatable wavelength filter wheel or moveable slide, which includes a plurality of optical filters having predefined transmit wavelengths. Therefore, the device is provided with a conventional filter bank, from which a filter having predefined transmission properties is chosen. Thus the abovementioned problem relating to using and availability of filters remain.
BioTek Instruments Inc. has published a Synergy™ 4 Multi-Detection Microplate Reader. The system is provided with a Xenon flash as its light source and it contains two double monochromators.
US 2007/0098594 discloses a fluorescence measurement apparatus where the excitation light is produced using discrete wavelengths obtainable by lasers. Thus, there is no need for wavelength filtering. A drawback of this arrangement is that the set of wavelengths which can be used for excitation is very limited.
Light emitting diodes have also been used in apparatuses designed for other purposes than fluorescence measurements. U.S. Pat. No. 5,475,221 discloses an apparatus having an array of LEDs and an Acousto-Optic Tunable Filter (AOTF) controlled by multiplexing means to obtain a broadband spectrometer. DE 19709377 discloses a luminescence measurement system having an ultraviolet LED as a light source. Light may be filtered before guiding it to a sample. The system allows for improved measurement of luminescence decay times. Neither of these apparatuses is suitable for fluorescence measurements.